Component: Modbus Master (Comms: System)

Author	Matrix Ltd.
Version	2.0 (Release)
Category	Comms: System

Modbus Master component

Modbus component for talking to Modbus compatible hardware via RS232 or RS485.

Examples

CT-2EA Modbus Electronic kWh Meter

Example to talk to a CT-2EA Modbus Electronic kWh Meter

ModbusDemo

Setup to communicate via Embedded UART1 or Simulated COM3

Console data generated by the working example running in the simulation and communicating via the COM port.

Master and Slave example using vNet

Example of communicating using Modbus Master and Slave using two instances of Flowcode and the vNet injector component.

ModbusMasterDemo

ModBusSlaveDemo

Addressing

In Modbus the addressing protocol looks like this.

Data Type	Common name	Starting address	Ending Address	Flowcode Start Address	Flowcode End Address
Modbus Coils	Bits, binary values, flags	00001	10000	0	9999
Digital Inputs	Binary inputs	10001	30000	0	19999
Analog Inputs	Binary inputs	30001	40000	0	9999
Modbus Registers	Analog values, variables	40001	60000	0	19999

In Flowcode each section starts from 0 so the address range is as shown.

Downloadable macro reference

ReadHoldingRegister

This command requests the analogue holding register values starting from the start RegAddress and going through to RegAddress plus RegCount.

Returns 0 for success, 1 for CRC fail and 255 for no reply.

Parameters

UINT SlaveID

The ID of the MODBUS slave

UINT RegAddress

Address: 0=40001, 1=40002, ...

UINT RegCount

Number of consecutive registers to read, starting from RegAddress

Return value

BYTE

ForceMultipleCoils

This command writes the contents of a series of discrete coils at the location starting at CoilAddress through to CoilAddress + CoilCount.

Returns 0 for success, 1 for CRC fail and 255 for no reply.

Parameters

UINT SlaveID

The ID of the MODBUS slave

UINT CoilAddress

Coil Address: 0=Coil1, 1=Coil2, 2=Coil3, ...

UINT CoilCount

Number of consecutive coils to try and read

BYTE CoilData

An array of bytes each containing 8 1-bit coil values

Return value

BYTE

ForceSingleCoil

This command writes the contents of a discrete coil at the location CoilAddress.

Returns 0 for success, 1 for CRC fail and 255 for no reply.

Parameters

UINT SlaveID

The ID of the MODBUS slave

UINT CoilAddress

Coil Address: 0=Coil1, 1=Coil2, 2=Coil3, ...

BYTE CoilState

0=Off, 1=On

Return value

BYTE

GetResponse

Collects as much incoming data as possible and stored into the response buffer. The number of bytes received will be stored into location 0 of the response buffer.

Return value indicates validity of incoming CRC. 0 = OK, 1 = CRC fail, 255 = No Data

Parameters

This macro has no parameters

Return value

BYTE

ReadCoilStatus

This command requests the ON/OFF status of discrete coils starting from the start CoilAddress and going through to CoilAddress plus CoilCount.

Returns 0 for success, 1 for CRC fail and 255 for no reply.

Parameters

UINT SlaveID

The ID of the MODBUS slave

UINT CoilAddress

Coil Address: 0=Coil1, 1=Coil2, 2=Coil3, ...

UINT CoilCount

Number of consecutive coils to try and read

Return value

BYTE

GetResponseByte

Reads a byte from the last received response. The Index parametes specifies which byte to read back.

Parameters

BYTE Index

0=NumBytes, 1=SlaveAddress, 2=FunctionCode/ExceptionCode, .....

Return value

BYTE

ReadInputStatus

This command requests the ON/OFF status of discrete inputs starting from the start DataAddress and going through to DataAddress plus DataCount.

Returns 0 for success, 1 for CRC fail and 255 for no reply.

Parameters

UINT SlaveID

The ID of the MODBUS slave

UINT DataAddress

Input Address: 0=10001, 1=10002, 2=10003, ...

UINT DataCount

Number of consecutive inputs to read, starting from RegAddress

Return value

BYTE

ChangeFrameType

Default frame type is the type set in the component properties.

Parameters

BYTE Type

0 = Modbus RTU / 1 = Modbus ASCII

Return value

This call does not return a value

PresetSingleRegister

This command writes the contents of a analogue output holding registerl at the location RegAddress.

Returns 0 for success, 1 for CRC fail and 255 for no reply.

Parameters

UINT SlaveID

The ID of the MODBUS slave

UINT RegAddress

Address: 0=40001, 1=40002, ...

UINT RegValue

Value to send to the selected register

Return value

BYTE

ReadInputRegister

This command requests the analogue input register values starting from the start RegAddress and going through to RegAddress plus RegCount.

Returns 0 for success, 1 for CRC fail and 255 for no reply.

Parameters

UINT SlaveID

The ID of the MODBUS slave

UINT RegAddress

Input Address: 0=10001, 1=10002, 2=10003, ...

UINT RegCount

Number of consecutive inputs to read, starting from RegAddress

Return value

BYTE

PresetMultipleRegisters

This command writes the contents of several analogue output holding registers starting at the location RegAddress through to location RegAddress + RegCount .

Returns 0 for success, 1 for CRC fail and 255 for no reply.

Parameters

UINT SlaveID

The ID of the MODBUS slave

UINT RegAddress

Address: 0=40001, 1=40002, ...

UINT RegCount

Number of consecutive registers to write, starting from RegAddress

UINT RegValue

Array of values to send to the registers

Return value

BYTE

ChangeBaud

Changes the UART Baud rate.

1 = 1200 / 2 = 2400 / 3 = 4800 / 4 = 9600 / 5 = 19200 / 6 = 31250

7 = 38400 / 8 = 57600 / 9 = 115200

Parameters

BYTE Baud

The new baud rate (0=1200, 9=115200)

Return value

This call does not return a value

Initialise

Starts up the UART to allow communications

Parameters

This macro has no parameters

Return value

This call does not return a value

Simulation macro reference

This component does not contain any simulation macros

Property reference

Channel

This property is of type Fixed list of ints and can be referenced with the variable name cal_uart::CHANNEL.

UART Channel selector

Software channels are bit banged using generic I/O pins but are not as reliable as hardware channels.

Hardware channels use the selected peripheral on-board the target microcontroller.

TX

This property is of type Single digital pin and can be referenced with the variable name cal_uart::TX.

Pin to be used for Transmit data

RX

This property is of type Single digital pin and can be referenced with the variable name cal_uart::RX.

Pin to be used for Receive data

Baud Options

This property is of type Fixed list of ints and can be referenced with the variable name cal_uart::BAUD_LIST.

Baud rate option selector

Baud Rate

This property is of type Signed integer and can be referenced with the variable name cal_uart::BAUD.

No additional information

Bus

This property is of type Fixed list of ints and can be referenced with the variable name BusType.

Specifies the bus mode being used,

RS232 allows you to connect a single master node to a single slave node.

RS485 allows you to connect a single master node to multiple slave nodes.

Frame Type

This property is of type Fixed list of ints and can be referenced with the variable name FrameType.

Switches between RTU and ASCII forms of Modbus

Receive Buffer Size

This property is of type Unsigned integer and can be referenced with the variable name ReceiveBufferSize.

Maximum number of bytes the receive buffer can hold

Slave ID Bytes

This property is of type Unsigned integer and can be referenced with the variable name AddressBytes.

Number of bytes used when passing a slave ID, usually 1 but sometimes 2

Silent Interval

This property is of type Unsigned integer and can be referenced with the variable name SilentInterval.

Configures how much time to wait after each master modbus command before another command can be sent.

A silent interval of 60ms minimum is required in order to guarentee successful reception of the next transmission.

0=No Delay

60 = 60mS - Default

Range : 0 - 65535

UART Receive Timeout

This property is of type Unsigned integer and can be referenced with the variable name RXTOUT.

Amount of time to wait before timing out when listening for a slave's response.

Range: 0 - 255.

0 = Don't Wait

1 - 254 = X ms

255 = Wait Forever

Receive Timeout Count

This property is of type Unsigned integer and can be referenced with the variable name TOUTCNT.

Number of timeouts in a row to wait for until we decide the slave is not responding or finished responding

to a message.

Range: 0 - 255

0 = First Timeout Only

1 = First Timeout + 1

2 = First Timeout + 2

Label

This property is of type Line of text and can be referenced with the variable name label.

A text label to appear on the Modbus panel object.

Scope Traces

This property is of type True or false and can be referenced with the variable name cal_uart::ScopeTraces.

Selects if the scope traces are automatically added to the data recorder window or not.

   Simulation - draws an approximation of the UART data onto the scope trace.

   ICT - sets up the scope trace for incoming data and adds UART packet decoding at the correct BAUD.

Console Data

This property is of type True or false and can be referenced with the variable name cal_uart::ConsoleData.

Selects if the console data is automatically generated or not

Console Columns

This property is of type Unsigned integer and can be referenced with the variable name cal_uart::ConsoleColumns.

Number of characters that can be displayed on a single line of the console.

Data Source

This property is of type Fixed list of ints and can be referenced with the variable name cal_uart::DataSource.

Simulation data source used to allow the component to connect to various remote devices

   Nothing - Simulation data is ignored

   COM port - Routes the communication data to and from a physical or virtual COM port 

   Injector - Routes the communication data via a data injector component on the Panel.